This invention relates generally to melt transfer webs and more particularly concerns an improved melt transfer web for transferring vinyl ink to surfaces of workpieces which surfaces are uneven.
It is well-known in melt transfer printing systems to print a pattern with printing inks having a thermoplastic binder onto paper and then to transfer the pattern onto a fabric or other surface under heat and pressure. Various releasable layer compositions have been developed to enhance efficient graphic pattern transfer onto fibrous or textile material workpieces without damaging physical properties, feel, and touch of the fabric. Such systems were developed in an attempt to overcome the problems associated with satisfying temperature requirements which may vary over a wide range as well as to accommodate the various steps of forming the transfer paper and of performing the heat transfer itself.
Margerum et al. patent 4,511,602 discloses a heat transfer web comprising a carrier substrate and a transfer layer of a pigmented polyolefin and a rosin ester. When the transfer layer is required to have any significant thickness, there is included in the transfer layer a low melting point wax or resin to provide flexibility. The transfer layer disclosed in the Margerum et al. patent is a polyolefin of low molecular weight, low softening point, and moderate viscosity.
Geurtsen et al. patent 4,555,436 discloses a heat transfer laminate which has a carrier substrate, a release layer, an optional barrier layer, an ink design, and a coating layer. During heat transfer the release layer splits from the carrier substrate and forms a protective coating over the transferred design. The release coating contains a montan wax, a rosin ester or hydrocarbon resin, a solvent, and ethylene-vinyl acetate copolymer having a low vinyl acetate content.
Martinovich patent 3,567,571 discloses a heat transfer laminate structure for transfer printing a thermoplastic resin article. The laminate includes a heat release film, a film of thermoplastic resin (polyolefin) compatible with the article to be printed, and an image to be transferred. Another optional resin film (polyolefin) may be laminated over the image itself. When the image is then transferred to the workpiece, it is protected by the two resin films.
Mizuno et al. patent 4,253,838 discloses a heat transfer printing sheet which incorporates a dye having poor heat transfer properties. The dye is mixed with an alkaline agent having a property of increasing the heat transferability property of the dye and a binder. A resin layer is coated over the dye through which the dye can be passed when the heat transfer is carried out. Alternatively, a resin layer may be provided between the dye and base sheet. The combination of a dye sandwiched between resin layers is said to achieve a superior color transfer and fastness.
Sideman patent 3,952,131 discloses a heat transfer print sheet having a polyolefin coating overlying the printed surface of the base sheet. A silicone release layer is provided on top of the polyolefin coating. The printed pattern on the base sheet transfers through the polyolefin coating upon application of heat and pressure. The polyolefin coating prevents the heat transfer print sheet from adhering to the surface of the workpiece, thereby allowing the printing to permeate into the interior of the workpiece to provide a wear-resistant print.
Keino et al. patent 4,515,849 discloses a transfer print sheet comprising a base sheet and a release resin layer with the ink pattern printed on the release resin layer. The pattern is printed with an elastic high polymer resin and pigment admixed therewith. The pattern is overlaid with a dissolving agent layer which will dissolve, erode, swell, and/or otherwise modify the synthetic fibers of the workpiece, thereby rendering the synthetic fabric to be printed locally receptive to the high polymer resin ink.
Magnotta patent 4,536,434 discloses a heat transfer laminate having a hot melt release layer, an ink layer, and an adhesive coating layer which is said to have improved release characteristics and to provide a protective coating on the imprinted article.
Magnotta patent 4,557,964 discloses a heat transfer laminate having the same basic structure as previously described in connection with the Magnotta patent 4,536,434 with an improved release coating which transfers the ink design and forms an optically clear protective coating over the transferred ink layer. The transferred release coating upon resolidification has an exceedingly high optical clarity with no hazing, spotting, or halo discernible over the transferred ink pattern. The release layer incorporates a tackifying resin in a wax base of montan wax and a crystalline wax such as paraffin wax.
Greenman et al. patent 4,235,657, which is assigned to the assignee of the present invention, discloses a melt transfer web useful for transfer printing graphic patterns onto natural synthetic fabric sheets. The transfer web of the Greenman et al. patent consists of a flexible substrate, a release layer applied to the top of the flexible carrier substrate, and a binder layer applied over the release layer. A pattern of ink is printed by conventional means on the binder layer. During the hot melt transfer process, the binder layer is released from the carrier substrate along with the ink and binds adhesively to the fabric to bind the ink to the fabric of the workpiece.
The transfer webs disclosed in the Greenman et al. patent can be used one on top of the other to print multiple-color patterns such as in the making of signs. For example, one web may be imprinted with a solid color (white for example) which is to be used for the letters in a sign, and the second web can be imprinted with a solid color (green for example) which is to be used for the background. The letters for the sign are cut out from the white web and laid on the workpiece surface. The green web is then laid over the letters. During the heat transfer process, the ink from both webs is transferred to the sign surface, producing white letters with a green background.
Because the release layer in the Greenman et al. patent includes a polyethylene wax, having a fairly low melt index, the wax in the webs used for the letters may seep out around the edges of the letters, thereby inhibiting printing of the background color adjacent the edges of the letters and producing a halo effect around the letters. The halo effect also results from the inability of the transfer web being used for the background color to conform around the thickness and edges of the transfer web which is used to print the underlying letters.